This invention relates to an improved method and arrangement for efficiently providing information to characterize an element by coding the values of a defined set of parameters for that element.
The accurate measurement of physical quantities such as pressure or flow are difficult enough under room temperature conditions. When these measurements are made in the outdoor environment, widely varying temperatures introduce errors because the output of typical transducers (devices which provide a usable output in response to a specific physical quality) unavoidably shifts slightly with changes in ambient temperature. For temperature transducers, this change is desired (indeed, often maximized). But for other transducers, this shift in transducer output owing to changes in ambient temperature is unwanted. This characteristic is referred to as the thermal shift. If given a numeric valve, the amount of shift is listed as the thermal coefficient (e.g., 0.02% change in output per degree of temperature).
Further, the thermal shift usually affects two different transducer characteristics--the zero output (the transducer output when the physical quantity is zero) and the sensitivity (the ratio of the change in transducer output to a change in the value of the physical quantity). Thus, thermal shifts are usually referred to separately as either thermal zero shifts or thermal sensitivity shifts, and are typically the result of several independent changes with temperature occurring in the transducer.
Even very expensive electrical transducers can be several percent in error at extremes of outdoor ambient temperatures of -40.degree. F. to +140.degree. F. The general practice of electrical transducer suppliers for improving accuracy is to use trimming components in a dedicated circuit to provide temperature compensation of the electrical output. Thus, a dedicated circuit assembly must be provided and fine tuned to the individual transducer characteristics. The cost of the temperature compensated electrical transducer increases accordingly. As a rule of thumb, to reduce the error by one half, the cost is likely to rise by a factor of four.
In applications where the output of an electrical transducer is the input to some form of digital computer-based system, compensation by internal software within the computer becomes practical. Temperature compensation by software is more cost effective than compensation by hardware in high accuracy applications. However, such cost effectiveness is severely degraded if there are unique compensation characterization numbers for each individual electrical transducer and the unique numbers have to be entered into the computer either manually by keyboard or by providing dedicated digital input circuitry with each transducer along with a digital input port in the system.
It is therefore an object of the present invention to provide a method and arrangement for providing information to a computer-based system to characterize an input element connected to the system.
It is another object of this invention to provide such an arrangement wherein the element is precalibrated so that such elements are interchangeable for connection to the system without any further calibration.